Kirk posted a statement on his blog Tuesday saying same-sex couples should have the right to civil marriage. He says what matters in life is who you love and "government has no place in the middle."

He is the second Republican in the U.S. Senate to back same-sex marriage.

Rick Garcia is director of the Equal Marriage Illinois Project. He says momentum is growing for marriage equality, especially among Republicans.

Opponents like Laurie Higgins of the Illinois Family Institute disagree. Higgins says Kirk and other Republicans who back gay marriage are contributing to the destruction of marriage and diminished religious liberty.